My images look really pixelated, no matter the resolution.

By default, WordPress compresses and resizes your images so that your site loads more quickly. This process degrades image quality. Here are several tips to improve image quality:

Don’t use blurry or pixelated images, but I’m sure you already know that 🙂

Instead, capture or source high quality and high-resolution photographs.
After doing so, if you’re trying to upload your images into blog posts, make sure to select the full-size option: http://prntscr.com/qd1kt3

When possible, resize your images to the required dimensions before uploading them to WordPress. I’d recommend taking a look at the article below, as we explain what are the recommended sizes: https://flothemes.com/flothemes-image-sizes/

Regardless of file format, use the RGB
(screen) color space. The CMYK color space is for print media.
Increase WordPress’ default JPEG image compression limit with the SimpleJPEGQuality plugin. You can find it here:https://wordpress.org/plugins/simplejpegquality/.

The last step would be to alter the sharpness of resized images with the Sharpen Resized Images plugin here: https://wordpress.org/plugins/sharpen-resized-images/.